CASSETTE FOR OPTICAL FIBRES

Abstract: A cassette being stackable in a coupling box for optical fibre cables. The bare fibres at the end portions of at least two fibre cables (F1, F2) are protectively stored in the cassette. The cassette comprises a radially external side wall (102a) which defines an internal storage space for the bare fibres. Two lead-through portions (108, 109) are formed as radial protrusions (108, 109) of the cassette, the configuration of which is like a circular disc. The radial protrusions are provided with two inlet openings (103a, 103b) facing circumferentially in opposite directions. Guiding means (104a, 104b) are disposed adjacent to the respective inlet opening so as to releasably secure the bare fibres of the respective cable end portion.

Description: CASSETTE FOR OPTICAL FIBRES Field of the invention The invention relates to a cassette for optical fibres of the kind stated in the preamble of claim 1. Prior art Such a cassette, shaped substantially as a circular disc, is previously known from the patent specification SE-B-457 021, wherein the fibre cables are placed with retained shields and with a number of loops in an external storage space, which is situated outside an external side wall and is externally free, wherefrom the cables are drawn with their bare end portions, i.e. with their bare fibres, via two helical lead-through portions through the side wall into a radially internal storage space. In this internal storage space, which is inwardly limited by an internal circular ring wall, the bare fibres are placed in curved, substantially circular loops up to a joining or branching place. Upon mounting of a circular lid, the fibres are securely protected inside the cassette. By such an arrangement of fibre cables and their end portions, it is possible to effectively protect the joining and branching places and to ensure that the bare fibres at the cable end portions are securely retained in well-defined positions in loops having a relatively large radius of bending curvature. This is very important in order to retain the transmission qualities of the optic fibres. A sharp bend, i.e. a small radius of curvature, will cause substantial losses. A cassette according to said patent specification SE-B-457 021 is relatively easy to handle, and the insertion of the fibre loops into the internal storage space can be carried out without serious problems. However, a careful handling is required, and it is necessary to observe great care and accuracy when removing the insulation and placing the fibre into the helical lead-through portion while securing the shielded cable loops in the external storage space, e.g. with an elastic string of cellular rubber. In the lead-through portion itself, the fibre must be secured in its groove by placing a piece of rubber in the upper part of the groove, so that the fibre can slide in the groove without engaging with the wall of the groove. Internal tensions in the fibre will also cause losses. Moreover, in the known cassette, it is difficult to prevent the cable from being bent sharply or being put under stress immediately outside the inlet openings of the cassette. The space between the inlet openings of the cassette, normally two such openings, and the inside of the two-part box, which encloses a number of cassettes stacked onto each other, is relatively narrow, and the operator must therefore exert great skill in order to secure that the cables are positioned without mechanical tension or sharp bends in this space. Recently, ribbon- or band-like fibre cables are being used to an increasing extent, i.e. cables with a number of fibres, e.g. up to twelve fibres, grouped into a ribbon or band. To avoid losses it is necessary to prevent such ribbons or bands from being twisted. However, the ribbon or band may be bent as a whole provided that the bending radius is sufficiently large, e.g. 35 mm. Objects of the invention Against this background, the main object of the present inven¬ tion is to achieve an improved cassette, which enables an easy insertion of a bare fibre or fibre band into the cassette, a greater bending radius of the fibre loops in the storage space of the cassette, a secure holding of the end portions or bare fibres or fibre bands of the cable at the two inlet openings of the cassette, so that the risk of causing sharp bends or tensions is reduced outside as well as inside the cassette. Additional objects are to enable a deflection of a fibre loop into an opposite circum¬ ferential direction inside the cassette, and - a very swift and easy handling of the fibre loops when inserting the same into the cassette and taking them out again. Summary of the invention The above-stated main object is achieved for a cassette according to the invention, the features of which are stated in claim 1. Further advantageous features are stated in the depending claims 2 through 17. Thanks to the radial protrusion at the circumference of the cassette and the guiding means adjacent to each inlet opening at the protrusion, the cable end portion, possibly in the form of a bare fibre or fibre band, may be inserted in a simple manner into the cassette and be held in a well-defined posi¬ tion, which secures that the fibre loops will obtain a large bending radius in this region and will be situated at a dis¬ tance from the external side wall of the cassette immediately outside the inlet opening as well as immediately inside the inlet opening. Hereby, mechanical tensions and associated losses will be avoided. Further features and advantages with the invention will be apparent from the following detailed description. Brief description of the drawings The invention will be explained more fully below with reference to the appended drawings illustrating the a preferred embodi- ment. Fig. 1 illustrates in a perspective view a lid of a cassette according to the invention; Fig. 2 illustrates in a perspective view a cassette according to the invention (to which the lid of figure 1 fits) ; Fig. 3 illustrates in a planar view the cassette according to figure 2 with two inserted optical fibre bands and a joint; and Fig. 4 shows schematically in a planar view a modified embodi¬ ment of the cassette. Description of a preferred embodiment The preferred embodiment of the cassette and the associated lid, as illustrated in figures 1 and 2, is intended to be used essentially in the same way as the cassette according to the above-mentioned patent specification 457.021. Normally, a number of such cassettes, e.g. six of them, are stacked one on top of the other in a two-part cable box. The latter may be of the same kind as described in said patent specification and does not form any part of the present invention. Two or more optic fibre cables, which are to be joined to each other and/or form a branch, are inserted in sealed lead-through portions in the cable box, and the end portions of the cables are inserted into the cassette, where they form loose, curved loops and are mutually joined to each other or branched. The cassette 100 according to the present invention, like the previously known embodiment, is manufactured by injection moulding of thermoplastic material and has a substantially circular configuration. Thus, it is made up of a substantially circular disc-like bottom wall 101, which at its outer peri¬ phery has an upright, external side wall 102, inlet openings 103a, 103b, guides 104a, 104b adjacent to each inlet opening, various internal guide elements (to be explained below) , a holding device 105 for connection sleeves and a central tubular hub 106, by means of which the cassette is threaded onto a non- illustrated pin in the cable box. Upon mounting of the lid 200, the external configuration of which corresponds to the external configuration of the cassette and which is provided with a central hole 206, the cassette can be stacked with its lid together with other cassettes in the cable box. The external side wall 102 follows the outer contour of the bottom wall 101 - compare also figure 3 - and forms a circular portion 102a, which extends in an angular region of about 120°, approximately rectilinear portions 102b and 102c adjoining thereto, each extending about 30°, and furthermore two adjoi¬ ning circular portions 102d and 102e, respectively, each extending in an angular region of about 60° relative to the circular centre point 107 (somewhat displaced from the tubular hub 106) but having a centre of curvature situated at a radial distance from these centres 106, 107, so that the respective corner point 102f, 102g is situated at a greater radial dis- tance from the circular centre 107 than the circular portion 102a. The side wall 102 ends in these corner points 102f, 102g, and the bottom wall 101 forms in these regions a step-like shoulder adjoining a radially recessed portion of a correspon¬ ding, circular side wall portion 102h, which extends in an angular region of about 60°, and there is also a small overlap¬ ping region of the side walls, each of about 10-15°. The side wall portion 102h is situated at the same radial distance from the circular centre 107 as the circular portion 102a. The circular arc portions 102a and 102h are thus concentric relative to the circular centre 107, whereas the centre point of the circular arc 102a (opposite to the holding device 105) and the corner points 102f, 102g are approximately situated on a circle having a larger radius with a centre in the tubular hub 106. The cassette will thus fit inside a cable box having an internal cylindrical space, the cylinder radius of which somewhat exceeds the radius of the last-mentioned circle having its centre in the tubular hub 106. In relation to the smaller circle with the circular centre 107, the external portions of the bottom wall 101 and the side wall portions 102b, 102c, 102d, 102e form ear-like protrusions 108, 109 which, inside the corner points 102f, 102g, form inlet openings for optical fibres between the partially (at a mutual radial distance) overlapping side wall portions 102d, 102e and 102h. These inlet openings, denoted with arrows 103a and 103b in figure 3, are tangentially directed and thus enable a well- defined guidance of the end portions or bare fibres of the cable through these openings 103a, 103b. In the embodiment according to figure 3, two fibre bands Fl and F2, each consisting of 12 separate fibres unified into a unit by means of an adhesive, are inserted through the openings 103a, 103b and are securely held somewhat inside the respective opening in guides 104a, 104b, which consist of an insert body 110 and 111, respectively, of plastic material, e.g. cellular rubber, with guiding grooves extending tangentially in relation to the circular centre 107. These guiding grooves 112 and 113, respectively, are also parallel to the side wall portions 102h and 102d and 102e, respectively, so the bands Fl and F2 are kept upright and are therefore drawn as full lines only in figure 3. As appears from figure 3, each fibre band Fl, F2 is securely held in position and extends at a distance outside the side wall portion 102a immediately outside the inlet opening 103a and 103b, respectively, (in the region between the openings 103a and 103b they are also somewhat twisted and bent downwards from the plane of the cassette, although this is not illu¬ strated in figure 3, so that they adjoin smoothly from the lead-through openings of the enclosing cable box, the lead- through openings normally being situated in a different plane than the particular cassette) and extend further in parallel to and at a distance inside the external side wall portion 102d, 102e, respectively, of the ear-like protrusion 108, 109. From these protrusions 108, 109, the fibre bands Fl, F2 extend relatively close to the inside of the side wall portion 102a and extend further approximately in a circular arc adjacent to the opposite side wall portion 102h and, finally, approximately another half turn to the holding device 105, where they are connected in a joint in a connecting sleeve S, which is inserted into the space between two of the mutually parallel partitions 105a-g thereof. On the upper edges of the side wall portions 102a and 102h, there are a number of inwardly directed, relatively short holding tongues 113a, 113b and 113c, 113d, respectively, and three elongated holding tongues 114a, 114b, 114c, by means of which the loop-formed fibre bands Fl, F2 are held in position when the cassette is being handled. Thus, the cassette may be handled at will and may even be turned upside down without involving any risk that the fibre bands fall out. When the fibre bands Fl, F2 are to be inserted into the cas¬ sette, the elongated holding tongues 114a, 114b, 114c are swung up about hinges formed by material recesses adjacent to the side wall 102a, 102h, so that the loops can be inserted from above and be secured in the guiding grooves of the insert bodies 110, 111 and be inserted below the fixed, shorter holding tongues 113a, 113b, 113c, 113d. The width of the fibre bands Fl, F2 (or height thereof when oriented upright as in figure 3) is substantially smaller than half the height of the side walls 102a-102h, so that the bands may cross each other, as shown in figure 3 adjacent to the tongues 114a and 113d. It does not matter if the fibre bands Fl, F2 contact each other. The crucial matter is that they are kept practically without tension while being bent with a large bending radius and are not twisted out of their vertical orientation. The loops Fl, F2 are so long that they - before they are inserted into the cassette - may be placed with their ends in a special joining apparatus for optical fibres. In figure 3 for the sake of simplicity, only two fibre bands Fl, F2 , are illustrated. However, a large number of fibre bands may be inserted, in particular pairwise, into the inlet ope¬ nings 103a, 103b and be laid in circular loops with joints in the holding device 105. A number of guiding pins 115a, 115b, 115c, 115d, 115e, 115f (six of them in the embodiment) serve as an internal guiding means in the radial direction, these guiding pins being arranged in a circle around the circular centre 107 and being provided with upper holding tongues 116a, 116b, 116c, 116d, 116e, 116f, which are parallel to the bottom wall 101 as are the other holding tongues. The guiding pins 105a-f are displaced circumferentially rela¬ tive to the elongated holding tongues 114a, 114b, 114c. These guiding pins 115a-f may also be used if one wishes to shift the circumferential direction of a fibre. In such a case, the fibre is inserted radially inwards past a guiding pin, e.g. 115a, past the central hole 107 and past an opposite guiding pin 115d at the other side, as indicated by a dotted line in figure 3. In order to achieve a further guidance at the inlet adjacent to the ear-like protrusions 108, 109, the guiding pins 117a and 117b, with each having a holding tongue 118a and 118b, respec¬ tively, are disposed at the same radial distance as the wall portions 102a and 102h. Thus, in principal, the whole storage space inside the external side wall 102a-102h can be used for protected storage of fibre loops. Moreover, the fibre loops may be arranged with a very large bending radius, namely approximately corresponding to the radius of the cassette. Upon mounting and securing the lid 200 shown in figure 1 (by means of non-illustrated screws) , the fibre loops are secured in position, though loosely, in their inserted positions. As an alternative to the guiding means 104a, 104b, the fibre loops may be secured in position at the respective inlet opening by means of threads or the like being inserted through holes 119 in the bottom wall 101. Apart from the holding device 105 or connecting sleeves, which are preferably inserted into the grooves between the partition walls 105a-g and are secured by means of non-illustrated locking bodies, e.g. pieces of plastic material, it is possible to dispose branching devices or other coupling devices in the rectangular recesses 120 and/or 121 in the bottom wall 101. As indicated in figure 4, the outer contour of the cassette 100 may be constituted by a large circular arc 102'a, extending along an angular region of about 300° and a radially recessed smaller circular arc 102 'h , extending along the remaining 60°, instead of the irregular configuration described above.

Claims: CLAIMS 1. A cassette (100) which is stackable in a coupling box for optical fibre cables so as to protectively store the bare end portions of at least two fibre cables (Fl, F2) , said cassette being shaped substantially as a circular disc and having a bottom wall (101) and a radially external side wall (102a) , which encloses an internal storage space for said protective storage of the bare fibres, wherein two lead-through portions (108, 109) are formed in the region of the external side wall so as to guide the end portions of the cables substantially tangentially into smoothly curved loops in the internal storage space, c h a r a c t e r i z e d i n that each lead-through portion is formed as a radial protrusion (108, 109) from the substantially circular configuration of the cassette, the external side wall (102d, 102e, 102h) is discon¬ tinuous in the region of each radial protrusion so as to form two inlet openings (103a, 103b) facing oppositely in circumferential directions, and guiding means (104a, 104b) are situated adjacent to each inlet opening for releasable securing of the bare fibres of each cable end portion in such a way that the fibres are held at a distance outside said external side wall (102h) and substantially parallel thereto immediately outside said inlet opening and at a distance inside said external side wall (I02d, 102e) and substantially parallel thereto immediately inside said inlet opening. 2. Cassette as defined in claim 1, c h a r a c t e r i z e d i n that said protrusions (108, 109) protrude as an ear from said circular configuration (102a, 102h) . 3. Cassette as defined in claim 2, c h a r a c t e r i z e d i n that the external side wall forms a smooth transition (102b, 102c) between said circular configuration (102a) and said ear-like protrusion (102d, 102e) . 4. Cassette as defined in claim 1, c h a r a c t e r i z e d i n that said radial protrusion is constituted by a step-like discontinuity (102f, 102g; 102'a, 102'h) of the radius of the cassette. 5. Cassette as defined in any one of claims 1-4, c h a r a c t e r i z e d i n that said external side wall (102) follows the periphery of the bottom wall around the whole cassette except for the region of the inlet opening (103a, 103b) . 6. Cassette as defined in claim 1, c h a r a c t e r i z e d i n that said internal storage space is substantially free all the way into the centre (107) , a number of guiding pins (115a) being disposed in an annular pattern around the centre so as to form an internal guidance of said curved loops and to enable a deflection of a loop into the opposite direction circumferentially. 7. Cassette as defined in claim 6, c h a r a c t e r i z e d i n that the guiding pins (115a etc) have upper holding tongues (116a etc) being substantially parallel to the bottom wall. 8. Cassette as defined in any one of claims 1-7, c h a r a c t e r i z e d i n that a number of elongated holding tongues (114a etc) extend radially inwards from the upper edge of said external side wall (102a, 102h) so as to retain said curved loops in the internal storage space when handling the cassette. 9. Cassette as defined in claims 7 and 8, c h a r a c t e ¬ r i z e d i n that said guiding pins (115a etc) and said elongated holding tongues (114a etc) are displaced relative to each other circumferentially in order to facilitate insertion of said curved loops into said internal storage space. 10. Cassette as defined in claim 8 or claim 9, c h a r a c ¬ t e r i z e d i n that said elongated holding tongues (114a etc) are foldable upwards and downwards. 11. Cassette as defined in any one of claims 1-10, c h a r a c t e r i z e d i n that a number of shorter holding tongues (113a-d) extend radially inwards from the upper edge of said external side wall (102a, 102h) . 12. Cassette as defined in claim 1, c h a r a c t e r i z e d i n that said guiding means (104a, 104b) , adjacent the respec¬ tive inlet opening, are constituted by guiding grooves (112, 113) extending in parallel to said external side wall (102h) . 13. Cassette as defined in claim 12, c h a r a c t e r i z e d i n that said guiding grooves (112, 113) are formed in a detachable insert body (110, 111) . 14. Cassette as defined in claim 13, c h a r a c t e r i z e d i n that said insert body (110, 11) is made of elastic material, e.g. cellular rubber. 15. Cassette as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that said holding device (105) for connecting sleeves (S) is disposed in said internal storage space symmetrically between said inlet openings (103a, 103b) . 16. Cassette as defined in claim 15, c h a r a c t e r i z e d i n that said holding device comprises a number of recti- linear, upwardly open grooves (between 105a etc) , extending substantially in parallel to said external side wall (102a) . 17. Cassette as defined in claim 16, c h a r a c t e r i z e d i n that said rectilinear grooves of said holding device (105) are dimensioned to freely receive said connecting sleeves (S) , the latter being secured in position by inserting a locking body of elastic material in the respective groove on top of an inserted connecting sleeve.

Inventors: OERJES ANDERS, OERJES, ANDERS
Applicants: OERJES ANDERS, TYKOFLEX AB, OERJES, ANDERS
Application year: 1994
Main classification: G02B6
IPC codes: G02B6